This invention relates to a novel silver halide crystal, application of a spectral sensitizing dye to said silver halide crystal, a process for preparation of said silver halide crystal and a silver halide photographic light-sensitive material.
Monodisperse silver halide crystals of ordinary shape useful in photography can be produced by the technique called the controlled double-jet precipitation which comprises introducing separate flows of an aqueous solution of a water soluble silver salt and an aqueous solution of a water soluble salt of an alkali metal halide into a gelatin solution under stirring, the process being controlled so as to adjust the shape of the produced silver halide crystal.
Core-shell structure of silver halide grains is reported in many literatures. Typically, the whole surface of the core is covered with one or more layers or "shells" of different silver halides.
It has been known for a long time to change the ratio of the halides and to use both the sensitized and unsensitized core-shell emulsions.
Furthermore, epitaxial mixed silver halide crystals possessing the radiation sensitivity of silver iodide and rapid developability of silver chloride in combination are disclosed in Japanese Patent Unexamined Publication No. 103725/78 and mixed silver halide cubic crystals having different silver halide composition in corner and body portions are disclosed in Japanese Patent Examined Publication No. 124139/80. However, the specific crystal of this invention has not been disclosed in any literatures.
For not only the crystals, but also photographic light-sensitive materials, there are strong demands for enhancement of sensitivity, contrast, etc. to improve the performance thereof. Moreover, development of light-sensitive materials of low silver content has also been strongly required for saving of resource of expensive silver. In order to meet these demands, it is essentially necessary to increase the sensitivity of silver halide photographic light-sensitive materials and this is the most important task for photographic industry.
As is well known, the inherent spectral sensitivity of wavelength region of silver halide per se is limited to short wavelength region of ultraviolet radiation or blue light. Sensitivity in such region can be increased by so-called chemical sensitization, but the wavelength region of sensitivity can hardly be changed. As methods for increasing sensitivity by chemical sensitization there are known sulfur sensitization, noble metal sensitization (for example, gold, palladium, platinum, iridium and selenium sensitizations), reduction sensitization, etc. and combinations thereof.
Extension of wavelength region of spectral sensitivity is accomplished by addition of sensitizing dyes to emulsions and this is known as spectral sensitization. It is known to use spectral sensitizing dyes such as cyanine dyes, e.g., nonmethine dyes, monomethine dyes, dimethine dyes and trimethine dyes alone or in combination (e.g., supersensitization) as spectral sensitizers.
These methods are disclosed in U.S. Pat. Nos. 2,688,545, 2,912,329, 3,397,060, 3,615,635, 3,628,964 and 3,672,898, British Pat. Nos. 1195302, 1242588 and 1293862, German Patent Publication Nos. (OLS) 2030326 and 2121780 and Japanese Patent Examined Publication Nos. 4936/68 and 14030/69.
Spectral sensitization is interpreted by the relative positional relation of energy levels of valence band and conduction band of silver halide crystal with molecular energy level of dye. This is explained in detail in "Photographic Science and Engineering" Vol. 18, pages 49-53, 175-178 and 475-485 (1974) and Vol. 24, pages 138-143 (1980).
However, from the practical viewpoint of spectrial sensitization effect, it is known that the spectral sensitizing effect is influenced by adsorption state of dye to the surface of silver halide crystal and further by chemical sensitizing effect and thus it is the important tasks of spectral sensitization technique for increasing the sensitivity of silver halide photographic light-sensitive materials to bring these requirements under optimum conditions.